Additive For Lubricant

ABSTRACT

An additive for lubricants exhibiting high oxidation stability, high thermal stability, and high No x  resistance, and having excellent functions as an extreme-pressure additive or wear-resistant agent and a lubricant composition containing the additive are provided 
     The present invention provides an additive for lubricants comprising a phosphate ester derivative represented by the general formula [I]: 
     
       
         
         
             
             
         
       
     
     wherein Y represents sulfur (S) or oxygen (O); R 1  represents a monovalent organic group having 4 to 24 carbon atoms; R 2  represents a divalent organic group having 1 to 6 carbon atoms; and n represents an integer of 1 to 3. The present invention also provides a lubricant composition containing the derivative.

TECHNICAL FIELD

The present invention relates to additives for lubricants. In particular present invention relates to an additive for lubricants comprising a novel phosphate ester derivative, a reaction product of the phosphate ester derivative with a zinc compound, or a mixture of the phosphate ester derivative with an organic zinc compound and to a lubricant composition containing the additive. This additive exhibits high oxidation stability, high thermal stability, and high No_(x) resistance, and has excellent functions as an extreme-pressure additive or wear-resistant agent.

BACKGROUND ART

During the operation of machinery, lubricant oils must have abilities of preventing or controlling galling of metal surfaces of machine parts caused by sliding or rolling contact therebetween. Additives, therefore, serve a significantly important role in improved wear resistance of lubricant oils and a prolonged service life of machinery.

Base oils cannot, by themselves, satisfy a variety of particular properties required for a wide range of lubricant compositions such as lubricant oils for internal-combustion engines and drive systems. Thus, additives for lubricant oils must be used in order to improve characteristics essential for lubricant compositions. Lubricant oils having one or more of these characteristics suitable for use in such lubricant compositions have been studied.

For example, Patent Document 1, as lubricant oil, discloses phosphorus- and sulfur-containing phosphate ester compounds represented by the general formula:

wherein R represents a saturated aliphatic hydrocarbon group having 2 or 3 carbon atoms, each X independently represents oxygen or sulfur, and each R′ represents an alkyl group having 1 to 18 carbon atoms. This document, however, does not disclose actual applications of this compound.

Patent Document 2 discloses a phosphoric ester derivative represented by the general formula:

wherein A represents an alkylene group having 2 to 6 carbon atoms, and each R′ represents an alkyl group having 2 to 4 carbon atoms. This compound is copolymerized with an acrylic ester for an application as a flame proofing agent.

Patent Document 3 discloses an ester-based lubricant composition containing an aromatic amine and an organic thiophosphate or thiophosphite represented by the general formula:

wherein X is O or S (at least one being S), m=0 or 1 (at least three m′s being 1), and each R represents an alkyl or aromatic group. This composition is used as antioxidant.

Patent Document 4 discloses a phosphorus- and sulfur-containing compound represented by the general formula:

Ya-S—Yb

wherein Ya corresponds to:

wherein Z represents a hydrocarbyl group, each R represents, for example, a hydrocarbyl or hydrocarbyloxy group, and R′ represents a hydrogen atom or a divalent hydrocarbyl group; X represents sulfur or oxygen, and Yb represents, for example, a hydrocarbyl group. This compound is used as antioxidant and an anti-wear additive.

Patent Document 5 discloses an alkylthiophosphate ester represented by the general formula:

wherein R represents, for example, an alkyl or cycloalkyl group, R′ represents an alkyl group, x represents 1 to 4, m represent 1 or 2, and m+m′=3. This ester is used as a corrosion inhibitor for ferrous metals.

Patent Document 6 discloses an alkoxypolyethyleneoxy acid phosphite ester represented by the general formula:

RO—(CH₂CH₂O)_(x)P(R′)—OH

wherein R represents an alkyl or alkenyl group, R′ represents, for example, an alkoxy group, x represents 2 to 4. This ester is used as an additive that improves water permissible range of oil.

Patent Document 7 discloses a cyclic phosphate represented by the general formula:

wherein R represents, for example, an alkyl group, R′ represents an alkylene group, X represents O, NH, or S, m represents 1 to 3, m′ represents 1 to 12, and m″, represents 0 or 1. This phosphate is used as an anti-wear additive, antioxidant, and friction modifier for lubricant compositions such as automotive transmission fluids.

Patent Document 8 discloses a phosphorus and nitrogen containing derivative of a sulfur-containing compound prepared by reacting at least one sulfur composition with a di- or tri-hydrocarbyl phosphite and/or an amine compound. This derivative is an additive useful for fuel, lubricant, and functional fluid compositions.

Patent Documents 9 and 10 disclose a reaction product of (1) a β-hydroxythioether reactant, (2) dihydrocarbyl hydrogen phosphite, trihydrocarbyl phosphite, or a mixture thereof, and (3) a compound containing a specific nucleophilic group. These products are used as anti-wear agents and antioxidants.

Patent Document 11 discloses phosphorus- and sulfur-containing phosphite compounds represented by the general formula:

(R—X′—R′—Y′)_(m)—P—(OH)_(3-m)

wherein X′ represents S (sulfur), Y′ represents S (sulfur) or O (oxygen), R represents an organic group having 6 to 20 carbon atoms, R′ represents an organic group having 1 to 6 carbon atoms, and m represents an integer of 1 to 3; and the general formula:

wherein X′, Y′, R, and R′ are defined as above, p represents an integer of 0 to 2, and q represents an integer of 0 or 1, p and q being not 0 at the same time.

Patent Document 12 discloses a composition prepared by heating an imide dispersion containing boron and a phosphate and/or phosphite represented by the general formula:

A-(RO)—(R′O)—P—(O)_(m)

wherein A represents H or OH, m represents 0 or 1, A is OH when m is 0 or H or OH when m is 1, and R and R′ each represent H or hydrocarbon containing at least one S or O atom.

Patent Document 13 discloses a phosphate compound represented by the general formula:

wherein R′s each represent a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms, X′s each represent oxygen or sulfur, and Z represents a metal atom. This compound is used as an anti-wear additive with base value retention property.

Lubricant oils containing these conventional additives, however, do not exhibit satisfactory extreme-pressure properties, wear resistance, or friction characteristics under severe conditions of heavy load.

Patent Document 1: U.S. Pat. No. 2,750,342 Patent Document 2: U.S. Pat. No. 2,960,523 Patent Document 3: U.S. Pat. No. 3,446,738 Patent Document 4: U.S. Pat. No. 4,081,387 Patent Document 5: U.S. Pat. No. 4,511,480 Patent Document 6: U.S. Pat. No. 4,579,672 Patent Document 7: U.S. Pat. No. 4,776,969

Patent Document 8: WO88/03554 Patent Document 9: WO89/12666 Patent Document 10: JP-T-Hei3-500061 Patent Document 11: JP-A-Hei11-171892

Patent Document 12: U.S. Pat. No. 6,352,962

Patent Document 13: JP-A-2002-294271 DISCLOSURE OF INVENTION Problems to be Solved by the Invention

An object of the present invention that has been made under such circumstances is to provide a novel sulfur-containing organic phosphorus compound and an additive for lubricant oils containing the compound, and to provide a lubricant composition exhibiting excellent extreme-pressure properties, wear resistance, and friction characteristics under severe operation conditions of heavy load in internal-combustion engines and drive system machines.

Means for Solving the Problems

The inventors intensively studied to achieve the object described above; discovered that a specific phosphate ester derivative exhibited excellent thermal stability, oxidation stability, No_(x) resistance, and base value retention property and was useful as an extreme-pressure agent, an anti-wear agent, and a friction modifier; and completed the present invention.

Accordingly, the present invention provides the following additives for lubricants and the like:

1. An additive for lubricants comprising a phosphate ester derivative (A) represented by the general formula [I]:

wherein Y represents sulfur (S) or oxygen (O); R¹ represents a monovalent organic group having 4 to 24 carbon atoms; R² represents a divalent organic group having 1 to 6 carbon atoms; and n represents an integer of 1 to 3. 2. An additive for lubricants comprising a reaction product of a zinc compound (B) with a phosphate ester derivative (A) represented by the general formula [I]:

wherein Y represents sulfur (S) or oxygen (O); R¹ represents a monovalent organic group having 4 to 24 carbon atoms; R² represents a divalent organic group having 1 to 6 carbon atoms; and n represents an integer of 1 to 3. 3. An additive for lubricants comprising a mixture of an organic zinc compound (C) and a phosphate ester derivative (A) represented by the general formula [I]:

wherein Y represents sulfur (S) or oxygen (O); R¹ represents a monovalent organic group having 4 to 24 carbon atoms; R² represents a divalent organic group having 1 to 6 carbon atoms; and n represents an integer of 1 to 3. 4. The additive for lubricants described in one of Aspects 1 to 3, wherein Y in the phosphate ester derivative represented by the general formula (I) is oxygen (O). 5. The additive for lubricants described in Aspect 2, wherein the zinc compound (B) is at least one compound selected from the group consisting of zinc metal, zinc oxide, organic zinc compounds, zinc salts of oxyacids, zinc halides, and zinc complexes. 6. The additive for lubricants described in Aspect 2, wherein the zinc compound (B) is at least one compound selected from the group consisting of zinc, zinc oxide, zinc hydroxide, zinc carbonate, dimethylzinc, diphenylzinc, and zinc complexes. 7. The additive for lubricants described in Aspect 3, wherein the organic zinc compound (C) is at least one compound selected from the group consisting of zinc alkylcarboxylates, zinc alkenylcarboxylates, zinc alkylphenylcarboxylates, and zinc alkenylphenylcarboxylates. 8. The additive for lubricants described in Aspect 3, wherein the organic zinc compound (C) is at least one compound selected from the group consisting of zinc oleate, zinc isostearate, zinc stearate, zinc alkylphenylcarboxylates, and zinc alkylsalicylates. 9. An additive composition for lubricants comprising the additive for lubricants described in any one of Aspects 1 to 8. 10. A lubricant composition comprising a lubricant base oil and the additive for lubricants described in any one of Aspects 1 to 8 in an amount of 0.001 to 0.5% by mass in terms of elemental phosphorus. 11. A lubricant composition for internal-combustion engines comprising a lubricant base oil and the additive for lubricants described in any one of Aspects 1 to 8 in an amount of 0.001 to 0.5% by mass in terms of elemental phosphorus. 12. A method of producing an additive for lubricants comprising reacting the phosphate ester derivative (A) with a zinc compound (B) described in Aspect 2 or 4.

ADVANTAGES OF THE INVENTION

The lubricant composition of the present invention exhibits superior base value retention in a No, atmosphere, namely, superior long drain capability, as well as excellent wear resistance and high-temperature detergency.

Accordingly, the composition is effectively used as lubricant oils for internal-combustion engines with a high No_(x) gas concentration and a relatively high-temperature atmosphere, for example, crankcase oils of internal-combustion engines such as petrol engines, diesel engines, and gas engines using natural gas, liquid petroleum gas (LPG), cracked gas, and coal cracked gas. The lubricant composition of the present invention is applicable to lubricant oils, such as transmission oils, gear oils, bearing oils, shock absorber oils, and industrial lubricant oils, which require base value retention property, wear resistance, and high-temperature detergency.

BEST MODE FOR CARRYING OUT THE INVENTION

A first aspect of the present invention is an additive for lubricants comprising a phosphate ester derivative (A) represented by the general formula [I] described above.

In the general formula [I], R¹ is preferably a hydrocarbon group having 4 to 24 carbon atoms and more preferably an alkyl group having 8 to 16 carbon atoms. If the number of the carbon atoms in R¹ is less than 4, the additive exhibits poor characteristics in solubility in oil, extreme pressure properties, wear resistance, friction property, and lubricity, and has strong corrosive action. Examples of R¹ include alkyl groups, such as a butyl group, a pentyl group, hexyl groups, heptyl groups, octyl groups, nonyl groups, decyl groups, undecyl groups, dodecyl groups, tridecyl groups, tetradecyl groups, pentadecyl groups, hexadecyl groups, heptadecyl groups, octadecyl groups, nonadecyl groups, and eicodecyl groups; cycloalkyl groups, such as a cyclohexyl group, methylcyclohexyl groups, ethylcyclohexyl groups, propylcycloalkyl groups, and dimethylcycloalkyl groups; aryl groups, such as a phenyl group, methylphenyl groups, ethylphenyl groups, propylphenyl groups, trimethylphenyl groups, butylphenyl groups, and naphthyl groups; arylalkyl groups, such as benzyl group, phenylethyl groups, methylbenzyl groups, phenylpropyl groups, and phenylbutyl groups.

In the general formula [I], R² is preferably a hydrocarbon group having 1 to 6 carbon atoms and more preferably an alkylene group having 1 to 4 carbon atoms. Examples of R² include divalent aliphatic groups, such as a methylene group, an ethylene group, a 1,2-propylene group, a 1,3-propylene group, butylene groups, pentylene groups, and hexylene groups; alicyclic groups having two bonding sites derived from alicyclic hydrocarbons, such as cyclohexane and methylcyclopentane; and phenylene groups.

Y represents sulfur (S) or oxygen (O), at least one S atom being contained in the general formula (I), and n represents an integer of 1 to 3, preferably 1 or 2, and more preferably 2.

Examples of the phosphate ester derivative represented by the general formula [I] includes tri(hexylthioethoxy) phosphate, tri(octylthioethoxy) phosphate, tri(dodecylthioethoxy) phosphate, tri(hexadecylthioethoxy) phosphate, di(hexylthioethoxy) phosphate, di(octylthioethoxy) phosphate, di(dodecylthioethoxy) phosphate, di(hexadecylthioethoxy) phosphate, mono(hexylthioethoxy) phosphate, mono(octylthioethoxy) phosphate, mono(dodecylthioethoxy) phosphate, and mono(hexadecylthioethoxy) phosphate.

Methods of producing the phosphate ester derivative represented by the general formula [I] are not particularly limited. For example, the phosphate ester derivative can be prepared by the reaction of hydrocarbylthioalkylalcohol represented by the general formula [II]:

R¹—S—R²—YH  [II]

wherein Y represents sulfur (S) or oxygen (O), and R¹ and R² are defined as above; or hydrocarbylthioalkoxide represented by the general formula [III]:

R¹—X—R²—YNa  [III]

wherein X, Y, R¹, and R² are defined as above; with phosphorus oxychloride (POCl₃) in the absence of catalyst or presence of a base.

The proportion of the hydrocarbylthioalkylalcohol or hydrocarbylthioalkoxide used in the reaction is generally 0.1 to 5.0 mol, preferably 1 to 3 mol, and more preferably 1.5 to 2.5 mol for 1 mol of phosphorus oxychloride.

The reaction temperature is selected within the range of generally −60° C. to 100° C. and preferably −30° C. to 50° C. The reaction may be carried out in the absence of catalyst or presence of a base. Examples of the base include triethylamine and pyridine. For the reaction, a solvent such as xylene, toluene, tetrahydrofuran (THF), or diethyl ether may be used.

In another example of the methods, the ester can be prepared by the reaction of alkylthioalkylalcohol represented by the general formula [II]:

R¹—S—R²—YH  [II]

wherein Y represents sulfur (S) or oxygen (O), and R¹ and R² are defined as above, with diphosphorus pentoxide (P₂O₅).

The proportion of the alkylthioalkylalcohol used in the reaction is generally 1 to 12 mol, preferably 2 to 6 mol, and more preferably 3 to 4 mol for 1 mol of diphosphorus pentoxide.

The reaction temperature is selected within the range of generally 0° C. to 140° C., preferably 30° C. to 110° C., and more preferably 50° C. to 90° C. For the reaction, a solvent such as xylene, toluene, THF, diethyl ether, or chloroform may be used.

A second aspect of the present invention is an additive for lubricants comprising a reaction product of the phosphate ester derivative (A) described above with a zinc compound (B).

The zinc compound (B) is preferably selected from zinc metal, zinc oxide, organic zinc compounds, zinc salts of oxyacids, zinc halides, and zinc complexes. Examples of the zinc compound include zinc, zinc oxide, zinc hydroxide, zinc carbonate, zinc dimethyl, zinc diphenyl, and zinc complexes.

The reaction of the phosphate ester derivative (A) with the zinc compound (B) can be carried out in the absence or presence of a catalyst. The proportion of the phosphate ester derivative used in the reaction is generally 0.1 to 5.0 mol, preferably 1 to 3 mol, and more preferably 1.5 to 2.5 mol for 1 mol of zinc compound.

The reaction temperature is selected within the range of generally room temperature to 200° C. and preferably 40° C. to 150° C. For the reaction, a solvent such as xylene, toluene, or hexane may be used.

A third aspect of the present invention is an additive for lubricants comprising a mixture of the phosphate ester derivative (A) described above and an organic zinc compound (C).

The organic zinc salt (C) is preferably selected from zinc alkylcarboxylates, zinc alkenylcarboxylates, zinc alkylphenylcarboxylates, and zinc alkenylphenylcarboxylates. Examples of the organic salt include zinc oleate, zinc isostearate, zinc stearate, zinc alkylphenylcarboxylates, and zinc alkylsalicylates.

As described above, the phosphate ester derivative (A) can be used alone as the additive for lubricants, and is preferably used in the form of a reaction product of the component (A) with the zinc compound (B) or a mixture of the component (A) and the organic zinc compound (C). These reaction product and mixture may be used alone or in combination of two or more different types.

The effective amount of these additives depends on applications. In general, these additives may be used in an amount of generally 0.001 to 1.0%, preferably 0.005 to 0.5% by mass, in terms of elemental phosphorus, of a base oil.

Examples of usable base oil include a variety of mineral oils and synthetic oils, which may be appropriately selected depending on applications. Examples of the mineral oils include paraffinic mineral oils, naphthenic mineral oils, and intermediate mineral oils, and more specifically include solvent-refined or hydro-refined light neutral oils, medium neutral oils, heavy neutral oils, and bright stocks.

Examples of synthetic oil include poly-α-olefins, α-olefin copolymers, polybutene, alkylbenzenes, polyol esters, dibasic acid esters, polyvalent alcohol esters, polyoxyalkylene glycols, polyoxyalkylene glycol esters, polyoxyalkylene glycol ethers, and cycloalkane compounds.

These base oils for lubricants may be used alone or in combination of two or more. Any combination of mineral oils and synthetic oils may also be available.

The additive composition for lubricants in accordance with the present invention may contain various components conventionally used in lubricant compositions, such as detergents and dispersants, antioxidants, rust inhibitors, antiforming agents, viscosity index improvers, pour-point depressants, demulsifying agents, other extreme-pressure agents, and anti-wear agents, within the scope of the object of the present invention.

EXAMPLES

The following examples illustrate the present invention, but do not serve to limit the scope of the invention in any way.

Example 1

Under a nitrogen stream, 13.2 g (0.55 mol) of sodium hydroxide and 100 mL of xylene were placed into a 500 mL flask, and 95.2 g (0.5 mol) of octylthioethanol in 100 mL xylene solution was added dropwise with stirring. The mixture was refluxed for five hours to promote the reaction.

Aside from this, 38.3 g (0.25 mol) of oxophosphorus chloride and 100 mL of THF were placed into an ice-cooled 1000 mL flask under a nitrogen stream, and the reaction mixture was added dropwise by spending two hours and was allowed to react for one hour at room temperature.

After 10 g (0.55 mol) of water was added dropwise to the resultant solution, the solution was stirred for one hour at room temperature and 100mL of water was added followed by stirring for one hour at room temperature. The solution was allowed to stand and the organic layer was separated from the aqueous layer. Into the organic layer, 100 mL of water was added followed by stirring. This cycle was repeated twice. Xylene and THF were distilled out from the organic layer, and the unconverted octylthioethanol and octylthioethyl chloride byproduct were removed by vacuum distillation. The yield of the resultant octylthioethyl phosphate was 75 g.

Example 2

After 45 g of actylthioethyl phosphate prepared in Example 1, 50 mL of toluene, and 1 g of water were placed into a 300 mL flask, the mixture was heated to 70° C. Next, 4.1 g (0.05 mol) of zinc oxide was added to the flask, and the mixture was allowed to react at 70° C. for three hours. Toluene and water were removed by vacuum distillation, and the residue was diluted with 15 g of mineral oil (150N equivalent), and the product was filtered. The yield of the reaction product was 60 g.

Example 3

The reaction was carried out as in Example 1 except that 123-3 g (0.5 mol) of dodecylthioethanol was used instead of octylthioethanol. The yield of the reaction product (dodecylthioethyl phosphate) was 92 g.

Example 4

The reaction was carried out as in Example 2 except that 55 g of dodecylthioethyl phosphate (the reaction product in Example 3) was used instead of the reaction product in Example 1. The yield of the reaction product was 70 g.

Example 5

The reaction was carried out as in Example 1 except that 81.1 g (0.5 mol) of hexylthioethanol was used instead of octylthioethanol. The yield of the reaction product (hexylthioethyl phosphate) was 61 g.

Example 6

The reaction was carried out as in Example 2 except that 33 g of hexylthioethyl phosphate (the reaction product in Example 5) was used instead of the reaction product in Example 1. The yield of the reaction product was 50 g.

Example 7

The reaction was carried out as in Example 1 except that 42.2 g (0.275 mol) of phosphorus oxychloride was used instead of 38.3 g (0.25 mol) of phosphorus oxychloride. The yield of the reaction product (octylthioethyl phosphate) was 62 g.

Example 8

The reaction was carried out as in Example 2 except that the reaction product in Example 7 was used instead of the reaction product in Example 1. The yield of the reaction product was 60 g.

Example 9

The reaction was carried out as in Example 1 except that 34.5 g (0.225 mol) of phosphorus oxychloride was used instead of 38.3 g (0.25 mol) of phosphorus oxychloride. The yield of the reaction product was 78 g.

Example 10

The reaction was carried out as in Example 2 except that the reaction product in Example 9 (octylthioethyl phosphate) was used instead of the reaction product in Example 1. The yield of the reaction product was 61 g.

Example 11

142.8 g (0.75 mol) of octylehioethanol and 500 mL of toluene were placed into a 1000 mL flask, and 35.0 g (0.25 mol) of diphosphorus pentoxide was added gradually. Then the system was stirred at 80° C. for six hours, and toluene was removed by vacuum distillation. The yield of the reaction product was 178 g.

Example 12

After 112.8 g (0.4 mol) of oleic acid, 16.2 g (0.2 mol) of zinc oxide, 50 mL of toluene, and 2 g of water were placed into a 500 mL flask, and the mixture was allowed to react at 70° C. for 3 hours. After toluene and water were removed by vacuum distillation, the residue was diluted with 30 g of mineral oil (150N equivalent) and the product was filtered. The yield of the reaction product was 145 g.

Example 13

The reaction was carried out as in Example 12 except that 113.6 g (0.4 mol) of stearic acid was used instead of oleic acid. The yield of the reaction product was 148 g.

Example 14

The reaction was carried out as in Example 12 except that 122.4 g (0.4 mol) of dodecylsalicylic acid was used instead of oleic acid. The yield of the reaction product was 156 g.

Examples 15 to 23 and Comparative Examples 1 and 2

According to the formulations shown in Table 1, the phosphate ester derivatives obtained in the above examples, a commercially available anti-wear agent or dibutyl phosphate, and various additives were added to 100N mineral base oil or 500N mineral base oil to prepare lubricant oil compositions of the present invention (Examples 15 to 23) and lubricant oil compositions for comparison (Comparative Examples 1 and 2).

TABLE 1 Composition of lubricant Example Example Example Example Example Example (parts by mass) 15 16 17 18 19 20 100N mineral oil*¹ 62.70 62.60 62.70 62.70 62.70 62.07 500N mineral oil*² 20.00 20.00 20.00 20.00 20.00 20.00 Compound of Example 1 — — — — — 1.20 Compound of Example 2 1.60 — — — — — Compound of Example 4 — 1.70 — — — — Compound of Example 6 — — 1.60 — — — Compound of Example 8 — — — 1.60 — — Compound of Example 10 — — — — 1.60 — Compound of Example 11 — — — — — — Compound of Example 12 — — — — — 1.03 Compound of Example 13 — — — — — — Compound of Example 14 — — — — — — Anti-wear agent*³ — — — — — — Dibutyl phosphate ester — — — — — — Viscosity index improver 5.00 5.00 5.00 5.00 5.00 5.00 Pour point depressant 0.50 0.50 0.50 0.50 0.50 0.50 Metal-based detergent*⁴ 3.20 3.20 3.20 3.20 3.20 3.20 Ashless dispersant A*⁵ 3.50 3.50 3.50 3.50 3.50 3.50 Ashless dispersant B*⁶ 1.00 1.00 1.00 1.00 1.00 1.00 Antioxidant*⁷ 2.00 2.00 2.00 2.00 2.00 2.00 Other additives*⁸ 0.50 0.50 0.50 0.50 0.50 0.50 Phosphorus content in 0.084 0.082 0.082 0.084 0.084 0.082 composition (mass %) Composition of lubricant Example Example Example Comparative Comparative (parts by mass) 21 22 23 Example 1 Example 2 100N mineral oil*¹ 62.10 61.52 62.07 63.30 62.72 500N mineral oil*² 20.00 20.00 20.00 20.00 20.00 Compound of Example 1 1.20 1.20 — — — Compound of Example 2 — — — — — Compound of Example 4 — — — — — Compound of Example 6 — — — — — Compound of Example 8 — — — — — Compound of Example 10 — — — — — Compound of Example 11 — — 1.20 — — Compound of Example 12 — — 1.03 — — Compound of Example 13 1.00 — — — 1.00 Compound of Example 14 — 1.58 — — — Anti-wear agent*³ — — — 1.00 — Dibutyl phosphate ester — — — — 0.58 Viscosity index improver 5.00 5.00 5.00 5.00 5.00 Pour point depressant 0.50 0.50 0.50 0.50 0.50 Metal-based detergent*⁴ 3.20 3.20 3.20 3.20 3.20 Ashless dispersant A*⁵ 3.50 3.50 3.50 3.50 3.50 Ashless dispersant B*⁶ 1.00 1.00 1.00 1.00 1.00 Antioxidant*⁷ 2.00 2.00 2.00 2.00 2.00 Other additives*⁸ 0.50 0.50 0.50 0.50 0.50 Phosphorus content in 0.082 0.082 0.082 0.082 0.085 composition (mass %)

(Note)

1: Refined hydrotreated mineral oil. Kinematic viscosity at 100° C., 4.5 mm²/s. Sulfur content; less than 0.0% by mass. 2: Refined hydrotreated mineral oil. Kinematic viscosity at 100° C.: 10.9 mm²/s. Sulfur content; less than 0.01 mass %. 3: Zinc secondary-dialkyldithiophosphate. Phosphorus content: 8.2% by mass. Zinc content: 9.0% by mass. Sulfur content: 17.1% by mass. 4: Calcium salicylate. Ca content: 7.94% by mass. 5: Polybutenyl succinic imide. Nitrogen content: 1.56% by mass. 6: Polybutenyl succinic imide, borate. Nitrogen content: 1.76% by mass. Boron content: 2.0% by mass. 7: Mixture of dialkyldiphenylamine and hindered phenol antioxidant. 8: Metal deactivator, antiforming agent, demulsifying agent etc.

The prepared compositions were each subjected to No_(x) resistance test, cam lifter wear test, and Falex test.

(1) No_(x) Resistance Test

Nitrogen monoxide (NO) gas (concentration: 8000 ppm) at 6 L/hr and air at 6 L/hr were injected into 250 mL of sample oil in the presence of iron-copper catalyst (test piece for oxidation test JIS K-2514). The sample was maintained at a temperature of 140° C. and the base value (hydrochloric acid method) after accelerated deterioration was measured. A smaller reduction in the base value refers to higher base value retention in a nitrogen oxide gas atmosphere, which is used in internal-combustion engines. Lubricant oils with higher base value retention can be used for longer time periods.

(2) Cam Lifter Wear Test

A JASO M328-95 cam lifter wear test was carried out to measure rocker arm pad scuffing area, rocker arm wear, and cum wear after 100 hour testing. For each testing, a lubricant composition having a value of 10 or less exhibits superior wear resistance.

(3) Falex Test

After running-in for 5 minutes under the conditions of pin material: AISI-3153, block material: AISI-1137, oil volume: 300 mL, number of rotations: 290 rpm, oil temperature: 100° C., and load: 1112 N, the load was continuously increased at a oil temperature of 100° C. to measure seizure load according to ASTM D3233. Lubricant oil having higher seizure load exhibits superior load-carrying capacity.

TABLE 2-1 Example Example Example Example Example Nox resistance test 15 16 17 18 19 Base value after Nox After 96 2.12 2.05 2.15 2.15 2.02 resistance test hours (Hydrochloric acid After 144 1.1 0.85 1.15 1.12 0.93 method) mgKOH/g hours

TABLE 2-2 Example Example Example Example Comparative Comparative Nox resistance test 20 21 22 23 Example 1 Example 2 Base value after Nox After 96 2.05 1.98 2.21 2.02 1.21 2.05 resistance test hours (Hydrochloric acid After 144 0.82 0.85 0.95 0.91 0.25 0.91 method) mgKOH/g hours

TABLE 3 JASO M 328-95 Example Example Comparative Comparative cam lifter wear test 15 20 Example 1 Example 2 Scuffing area of 8.5 5.4 9.3 10 rocker arm pad (%) Cum nose 6.7 6.9 26.8 6.7 wear (μm)

TABLE 4 Example Example Comparative Comparative Falex test 15 20 Example 1 Example 2 Seizure load N 3620 3800 3900 2400

The results of the Nox resistance test shown in Table 2 show that the lubricant compositions (Examples 15 to 23) of the present invention exhibit superior base value retention under the nitrogen oxide gas atmosphere. In contrast, Comparative Example 1 containing zinc dithiophosphate instead of the anti-wear agent of the present invention exhibits significantly poor base value retention.

The results of the cam lifter wear test shown in Table 3 show that the lubricant compositions (Examples 15 and 20) of the present invention exhibit superior wear resistance whereas Comparative Example 1 exhibits significantly poor wear resistance.

Comparative Example 2 exhibits satisfactory base value retention under the nitrogen atmosphere (Table 2) and satisfactory wear resistance (Table 3), but the load-carrying capacity is significantly inferior to that of the lubricant oil compositions (Examples 15 and 20) of the present invention (Table 4).

INDUSTRIAL APPLICABILITY

The lubricant oil composition of the present invention can be used as, for example, lubricant oils for internal-combustion engines, transmission lubricant oils, gear oils, bearing oils, shock absorber oils, and industrial lubricant oils. 

1. An additive for lubricants comprising a phosphate ester derivative (A) represented by the general formula [I]:

wherein Y represents sulfur (S) or oxygen (O); R¹ represents a monovalent organic group having 4 to 24 carbon atoms; R² represents a divalent organic group having 1 to 6 carbon atoms; and n represents an integer of 1 to
 3. 2. An additive for lubricants comprising a reaction product of a zinc compound (B) with a phosphate ester derivative (A) represented by the general formula [I]:

wherein Y represents sulfur (S) or oxygen (O); R¹ represents a monovalent organic group having 4 to 24 carbon atoms; R² represents a divalent organic group having 1 to 6 carbon atoms; and n represents an integer of 1 to
 3. 3. An additive for lubricants comprising a mixture of an organic zinc compound (C) and a phosphate ester derivative (A) represented by the general formula [I]:

wherein Y represents sulfur (S) or oxygen (O); R¹ represents a monovalent organic group having 4 to 24 carbon atoms; R² represents a divalent organic group having 1 to 6 carbon atoms; and n represents an integer of 1 to
 3. 4. The additive for lubricants in accordance with any one of claims 1 to 3, wherein Y in the general formula (I) is oxygen (O).
 5. The additive for lubricants in accordance with claim 2, wherein the zinc compound (B) is at least one compound selected from the group consisting of zinc metal, zinc oxide, organic zinc compounds, zinc salts of oxyacids, zinc halides, and zinc complexes.
 6. The additive for lubricants in accordance with claim 5, wherein the zinc compound (B) is at least one compound selected from the group consisting of zinc, zinc oxide, zinc hydroxide, zinc carbonate, dimethylzinc, diphenylzinc, and zinc complexes.
 7. The additive for lubricants in accordance with claim 3, wherein the organic zinc compound (C) is at least one compound selected from the group consisting of zinc alkylcarboxylates, zinc alkenylcarboxylates, zinc alkylphenylcarboxylates, and zinc alkenylphenylcarboxylates.
 8. The additive for lubricants in accordance with claim 7, wherein the organic zinc compound (C) is at least one compound selected from the group consisting of zinc oleate, zinc isostearate, zinc stearate, zinc alkylphenylcarboxylates, and zinc alkylsalicylates.
 9. An additive composition for lubricants comprising the additive for lubricants in accordance with any one of claims 1 to
 8. 10. A lubricant composition comprising a lubricant base oil and the additive for lubricants in accordance with any one of claims 1 to 8 in an amount of 0.001 to 0.5% by mass in terms of elemental phosphorus.
 11. A lubricant composition for internal-combustion engines comprising a lubricant base oil and the additive for lubricants in accordance with any one of claims 1 to 8 in an amount of 0.001 to 0.5% by mass in terms of elemental phosphorus.
 12. A method of producing an additive for lubricants, comprising reacting the phosphate ester derivative (A) with the zinc compound (B) in accordance with claim 2 or
 4. 